Doctor blade for coating machines



1954 w. J. MONTGOMERY ETAL 2,695,004

DOCTOR BLADE FOR COATING MACHINES Filed March 2, 1951 !NVENTOR W|||| J. Montgomery BY W m RToylor ATTORNEY United States Patent DOCTOR BLADE FOR COATING MACHINES William J. Montgomery and William P. Taylor, Hamilton, Ohio, assignors to The Champion Paper and Fibre Company, Hamilton, Ohio, a corporation of Ohio Applicafion. March 2, 1951, Serial No. 213,628

6Claims. (Cl. 118-262) correspondingly long doctors.

The blade of the present invention, while more or less generally useful where doctor blades with rotating rod edges are desired, is particularly adapted to cooperate with a rubber surfaced .roll to control the thickness or",

and to smooth, a layer of coating material on the surface of the roll prior to transfer of the coating from the surface of the roll to the paper web.

In devices of that type, considerable difliculty has been encountered in the attempt to secure smooth uniform coating films by means of a doctor blade or rotating rod and it has not heretofore been possible to so control the thickness of the coating layer that it would be thicker or thinner at one or both ends of the roll when desired, as for example, to compensate for thinuor thick edges, respectively, of the paper web, in order to render the finished web of uniform thickness.

In accordance with the present invention, therotating doctor rod, the length of which is in general many times as great as its diameter, is supported throughout its working length ina holder which forms a bearing in which the rod rotates. This bearing grasps the rod by reaching around substantially more than half its circumference but leaves a portion of the surface of the rod exposed, and it is this exposed portion which serves to perform the doctoring operation. Associated with this holder is a cleaning or wiping device which is continuous throughout the working length of the rod, and continuously wipes or cleans the rod as it rotates. This holder is made flexible, preferably at least as flexible as the rod itself, in the direction of its width. This holder is, in turn, mounted on a substantially rigid machine member, or support, to which it is securely clamped. Means adapted to flex the said holder are provided, in association with said support, for adjusting the straightness of the rod and thereby the thickness of the coating along the length of the rod i. e. across the width of the paper web being coated.

The invention will be further described by reference to the accompanying drawing on which Fig. l is a sectional view of a blade made in accordance with the present invention.

Fig. 2 is a fragmentary side view of the rotating rod and holder, shown in Fig. 1.

Fig. 3 is a view similar to Fig. 1, but showing a modified arrangement of the invention.

Fig. 4 is a fragmentary side view, similar to Fig. 2, but showing the modified arrangement illustrated in F ig. 3.

Referring first to Figs. 1 and 2, the rotating doctor rod is designated 11. The holder is formed in two parts 12, 12 which grasp the rod between them, and are firmly clamped to a substantially rigid support 13 in any convenient manner as by means of a clamping plate 14 and a series of screws 15. A series of suitably spaced adjusting screws 16 threaded through a flange 17 on the support member 13, serve to adjust the position of holder 12 and rod 11 relative to the rubber-covered roll or other surface on which the doctor operates, the approxi' 2. mate position of which, in one instance, is indicated by broken lines .at 18.

It may at times be found convenient to provide shims at 19 between the two halves 12, 12 ofthe bearing to provide easy adjustment for Wear. Alternatively, the holder maybe made in a single piece instead of two, if desired. In case the width of holder 12, and the material of which it is made, are such as to render it less flexible than the rod 11, its flexibility can be increased, if desired, by cutting slots 21 at suitable intervals along its length. Holes 22 in holder 12, through which the clamping screws 15 extend, are preferably slotted to permit adjustment of the position of holder 12 by screws 16.

As illustrated in the drawing, the bearing portions of holders 12, 12 terminate in sharp edges 20, 20 which, when the rod is rotated, serve to scrape off any adherent coating material, thereby cleaning the rod to prevent coating material from beingcar'ried around and redeposited where it is not wanted.

It should be noted that the holder 12 grasps the rod 11 around substantially more than half its circumference and forms a bearing in which rod 11 is adapted to rotate, but that this bearing is open on one side exposing a portion, substantially less than 'half in the circumferential direction, of the cylindrical surface of rod 11, which portion constitutes the active or working portion of the doctor.

The actual width of the portion of the surface of rod 11 which is thus exposed, may be varied in accordance with the use for which the doctor is intended. It it is to operate on a thin layer of coating on a surface curved in a direction opposite to the rod'surface (as indicated at 18). and which does not deform in operation, only a narrow width of the rod need be exposed. On the other hand, if the doctor is to operate on a deep layer of coating, if the doctor is pressed against and indents the surface on which it operates (as in the case of the rubber roll described in the aforesaid application), or if the doctor is to operate on a web which wraps around its working edge, then a wider area of the surface must be exposed. The exposed area should, however, always be substantially less than half the circumferential area of the rod in order that the parts 12, 12 may hold the rod in position in its bearing and prevent its escape. For this purpose the bearing should preferably enclose at least 210 degrees and advantageously 240 degrees or more of the circumference of the rod.

In the present specification and claims, the word width in reference to the holder 12, is used to refer to the dimension from the exposed surface of rod 11 to the adjusting screws 16 while the word thickness is used to refer to the dimension between the support 13 and clamping plate 14. Theseterms are simply used to indicate briefly the direction in which the holder 12 is flexible, and are not to be understood to imply that the one dimension is necessarily greater than the other, since it may under some circumstances be found desirable to have the thickness greater than the width as above defined.

A slightly modified form of the invention is illustrated in Figs. 3' and 4. The doctor rod is designated 31- and the two halves of the holder are designated 32, 32. The support 33 is a substantially rigid machine member in itself or is rigidly attached to such a member. The holder 32, 32 is securely clamped to the support 33 by means of clamp plate 34 and a plurality of screws 35. Coatings applied to paper surfaces frequently have a total thickness of less than 0.001 inch and doctor blade adjustments of less than 0.0001 inch are frequently significant. Such fine adjustments are difiicult with the simple screws 16 even though provided with fine threads. For this reason the adjusting means shown in Fig. 3 differs somewhat from that illustrated in Fig. 1. In place of the simple adjusting screws 16, a differential screw 36 is used for the purpose of facilitating fine adjustment. Screw 36 is threaded through a flange on support 33 and is also internally threaded to receive a screw 37 which has a slightly finer thread than the external thread on screw 36, whereby one turn of screw 36 advances screw 37 by the difference between the leads of the two threads. In order that screw 37 may move holder 12 in either direction as screw 37 is moved by turning screw 36, a rectangular head 38 on screw 37 fits into corresponding rectangular grooves 39, 39 in parts 32, 32.

The sharp edges 40, 40 on the parts 32, 32 of the holder serve as before described to continuously scrape off coating material from the surface of rod 31 as it rotates. To assure more perfect cleaning of the rotating rod when the bearing becomes somewhat worn in service, a commercial type of packing such as is used for packing glands and joints is provided at 41.

The holes 42 in holder 32, through which clamp screws 35 are adapted to pass, are slotted or made large enough to provide room for adjustment of holder 32, as described.

In order to prevent rod 31 from being forcibly pulled out of its bearing between parts 3232 by unusual external forces applied to the ends of rod 31, we find it a valuable precaution to provide on each end of the holder 32 a full bearing 43 which prevents unusual strain on bearing 3232.

The doctor rod 11, or 31, may be made of any material suitable to the particular materials on which it is to operate. For use with aqueous paper coating compositions we prefer to make the doctor rod of a corrosionresistant and wear-resistant material such, for example, as chromium plated steel, or any of the suitable known alloys containing material proportions of chromium, nickel, cobalt, titanium, tungsten, molybdenum, or' similar hard and corrosion resistant alloying elements.

The holder 12, or 32, which forms the bearing in which the doctor rod rotates may be made of any suitable bearing material, selected with reference to the type of service required, the material of the rod and the nature of the coating materials or other materials in contact with which the bearings must operate. For use with the aqueous-adhesive-mineral-pigment coatings used for coating paper, we have found that a commercial fabriclaminated phenolic resin bearing material to be highly satisfactory.

In using the blade of the present invention, whenever the coating is observed to be too thick or too thin at any portion of the width of the web, whether due to lack of exact straightness of the doctor, to sag, or variation in diameter or hardness, of the cooperating roll or to other cause, it is merely necessary to adjust the corresponding screw or screws 16, or 36, in the appropriate direction until the desired uniformity is secured. It is this adjustment which is meant by the term adjustment of the straightness" of the blade as used in the present specification and claims. It may result in increasing or decreasing the conformity of the rod to a straight line, as may be required in any given case, to produce the desired degree of uniformity in thickness of coatings, or of final coated product.

Doctor blades constructed as described have been found to be highly satisfactory and durable in actual use, to produce smooth layers of coating, which may be extremely thin when required, and to be easily adjustable, without stopping operation, to give coatings of uniform thickness, or a thickness which deviates from uniformity in any desired manner.

We claim:

1. A doctor blade for operating on fluid aqueous paper coating compositions, comprising adhesive and mineral pigment, said blade comprising: a rotatable doctor rod of chromium plated steel; a holder, formed of fabric-laminated phenol-formaldehyde resin, which is flexible in the direction of its width, which encloses said rod around substantially more than half its circumference, leaving a minor proportion of its surface exposed to form the working surface of the doctor, and forms a bearing in which said rod is adapted to rotate, which bearing is continuous throughout the working length of said rod; and adjusting means adapted to flex said holder to adjust the straightness of said rod.

2. A doctor blade structure which comprises: a rotatable doctor rod; a holder, flexible in the direction of its width, which encloses said rod around substantially more than half its circumference and forms a bearing therefor, which is continuous throughout the working length thereof; adjusting means adapted to flex said holder to adjust the straightness of said doctor rod; a sharp edge on said holder in close contact with, and continuous throughout the length of, said rod, for continu ously cleaning the surface of said rod as it rotates; a strip of packing material, continuous throughout the working length of said rod, located in a recess in the bearing and in contact with the surface of said rod so as to continuously wipe the rod as it rotates.

3. A doctor blade structure which comprises: a rotatable cylindrical doctor rod; a holder which extends around substantially more than half the circumference of said rod, leaving a minor portion of its surface exposed to constitute its working surface, and forms a bearing,

continuous through the working length of said rod, in

which said rod is adapted to be rotated, said holder being flexible in the direction of its width; supporting and clamping means for securing said holder against apprcciable flexure in the direction of its thickness; and adjusting means adapted to adjust the straightness of said rod by adjusting the position of said holder, in the direction of its width, at intervals along its length.

4. The doctor blade of claim 3 wherein the holder is made more flexible, in the direction of its width, than is the doctor rod, by combining a holder of fabric laminated phenol formaldehyde resin, with a steel doctor rod.

5. The doctor blade of claim 3 wherein the holder is made more flexible, in the direction of its width, by cutting it, at intervals along its length, from its back edge fofiwards towards but not to the location of the doctor ro 6. The doctor blade of claim 3 wherein the holder is composed of two parts separated by a plane substantially diametral to the doctor rod, and held together in service by the said clamping means.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,312,034 Jones Aug. 5, 1919 1,661,174 Francis Mar. 6, 1928 2,214,787 Dickhaut et al Sept. 17, 1940 2,221,441 Charters Nov. 12, 1940 2,334,102 Kauppi et al. Nov. 9, 1943 2,398,844 Muggleton et al. Apr. 23, 1946 2,598,733 Warner June 3, 1952 FOREIGN PATENTS Number Country Date 474,828 Great Britain Nov. 1, 1937 

